Coated abrasives comprise a backing having abrasive grains bonded thereto by one or more binders. These binders typically comprise a glutinous or resinous adhesive, and may optionally contain one or more additives. Examples of resinous adhesives include epoxy resins, phenolic resins, urethane resins, acrylate resins, and aminoplast resins. Examples of additives include fillers, grinding aids, wetting agents, dispersing agents, pigments, coupling agents, and dyes.
In some applications, a grinding aid is included in the binder to improve the abrading characteristics of the coated abrasive. It is believed that the grinding aid has a significant effect on the chemical and physical processes of abrading, thereby providing improved performance. For example, Minnesota Mining and Manufacturing Company of St. Paul, Minn. has manufactured "REGALITE POLYCUT" coated abrasives that contain an overcoating of an epoxy resin with a potassium tetrafluoroborate grinding aid dispersed in the epoxy resin.
The binders previously referred to are typically applied by coating from an organic solvent. There are several advantages in coating a resinous binder from an organic solvent, rather than from water. The lower surface tension of organic solvents typically provides better wetting and better adhesion, lower viscosities, and better dispersions of the additives.
In recent years, however, there has been a need to coat these resins exclusively from water on account of increasingly stringent pollution legislation. Accordingly, it is desired to provide a coated abrasive article having an overcoating containing an epoxy resin and a grinding aid, wherein the epoxy resin can be coated from water.
U.S. Pat. No. 4,396,657 discloses a saturant for impregnating the multifilament yarns of a stitchbonded coated abrasive backing comprising an epoxy resin, a dicyandiamide, blocked isocyanates, and/or imidazole curing agents. The epoxy resin is capable of being coated from water.
U.S. Pat. No. 3,615,303 discloses a treatment for the backing of a coated abrasive. The treatment, referred to as an intermediate layer, comprises an epoxide resin mixture based on (a) 4,4'-dihydroxydiphenyl-2, 2-propane (Bisphenol A), (b) an epoxide resin based on Bisphenol A internally plasticized by a reaction with castor oil, (c) carbamic acid alkyl esters, and (d) a curing agent. This epoxide resin is capable of being coated from water.